You can create a scheduled timer which automatically adds itself to the runloop and starts firing:
Swift 2
NSTimer.scheduledTimerWithTimeInterval(0.5, target: self, selector: "timerDidFire:", userInfo: userInfo, repeats: true)
Swift 3, 4, 5
Timer.scheduledTimer(withTimeInterval: 0.5, target: self, selector: #selector(timerDidFire(_:)), userInfo: userInfo, repeats: true)
Or, you can keep your current code, and add the timer to the runloop when you’re ready for it:
Swift 2
let myTimer = NSTimer(timeInterval: 0.5, target: self, selector: "timerDidFire:", userInfo: nil, repeats: true)
NSRunLoop.currentRunLoop().addTimer(myTimer, forMode: NSRunLoopCommonModes)
Swift 3, 4, 5
let myTimer = Timer(timeInterval: 0.5, target: self, selector: #selector(timerDidFire(_:)), userInfo: nil, repeats: true)
RunLoop.current.add(myTimer, forMode: RunLoop.Mode.common)